What are chemical molecules that travel through the bloodstream to affect body systems called?

The correct answer is hormones, which are chemical messengers that travel through the bloodstream to affect various body systems. Hormones are produced by endocrine glands and play a crucial role in regulating numerous physiological processes, including metabolism, growth and development, tissue function, and mood. They exert their effects by binding to specific receptors on target cells, leading to a wide range of responses that help maintain homeostasis in the body.

Understanding the role of hormones is essential in veterinary medicine as they are involved in numerous conditions and treatments, impacting animal health significantly. For instance, insulin regulates blood sugar levels, and thyroid hormones control metabolism, making it vital for veterinarians to have knowledge of these substances in diagnosing and treating endocrine disorders in animals.